1. Technical Field
The technical field of this disclosure relates generally to a sliding door assembly to allow passengers to rapidly enter and exit transit cars, and more specifically, to hangers used to slidably mount doors at the entry portals of rail transit cars, commuter train cars and other transit vehicles.
2. Description of the Prior Art
For much of the twentieth century, various attempts were made to improve the function, durability and reliability of sliding doors, and in particular, hanger assemblies from which sliding transit car doors are suspended. Because of the rugged environment to which the transit cars are subjected, transit authorities must periodically overhaul existing cars and/or replace the cars entirely. The sliding doors of these new and refurbished transit cars must have the ability to operate with longer periods between maintenance. When maintenance is necessary, the sliding doors should provide easy access to serviceable parts, and, if necessary, be easy to replace.
Many existing transit car door hanger assemblies are heavy, difficult to install and replace, as discussed in Morton Manufacturing Co.""s U.S. Pat. No. 3,466,698, and are not able to be used with a variety of different styles of sliding transit car doors. This requires manufacturers to carry parts for several different types of hanger assemblies to meet the demands of different transit authorities. For example, while some transit cars have sliding doors which are flat, running perfectly perpendicular to the floor of the transit car, many other transit cars have curved sliding doors, creating special challenges from a door hanger design standpoint because the center of gravity of the curved door is not directly below the sliding support. Circular raceways, as opposed to ball bearing supports, were used in the door hangers for curved doors, but these did not perform satisfactorily. U.S. Pat. No. 3,740,898, also owned by Morton Manufacturing Co., addressed this problem by employing sliding blocks that also pivot about a horizontal axis, which prevents binding of the curved door during horizontal sliding movement.
Morton Manufacturing Co.""s U.S. Pat. No. 4,854,078 addressed problems associated with chattering of curved sliding doors along conventional door hanger assemblies, which undesirably resulted in maintenance and down-time, by using a pair of pivot blocks and a hanger bar design that could be easily retrofit in existing transit cars. However, these multi-part assemblies were costly and still required maintenance.
U.S. Pat. No. 4,915,032, attempts to address many problems associated with sliding door hanger assemblies, such as protecting against the accumulation of debris on bearing surfaces, difficulties in installation and adjustment, and poor durability. The ""032 patent shows a door hanger assembly that can be used with both curved and flat doors. The door hanger assembly uses cylindrical bearing modules oriented in a single tubular sheath, with one of the bearing modules being located at each end of the tubular sheath, and the tubular sheath maintaining a fixed distance between the two bearing modules. The hanger which supports the door is attached to the lower edge of the tubular sheath, and the sheath and associated bearing members are of substantial size and weight. While the hanger assembly shown in the ""032 patent may reduce the likelihood of debris collecting between the bearing modules by encasing the two bearing modules in the tubular sheath, build-up of some debris between the modules is inevitable, and the door hanger of the ""032 patent provides no means of access to the portion between the bearing members for cleaning. Another disadvantage is the difficulty of using the door hanger of the ""032 patent for transit car doors of various sizes. For example, a different length of a central portion within the tubular sheath must be used for the door hanger to work with doors of different sizes.
It is an object of certain embodiments of the present invention to overcome these and other shortcomings of the prior art.
The hanger assembly of certain embodiments of the present invention provides a light-weight, easy-to-install and easy-to-maintain system for reliably mounting sliding transit car doors which are substantially flat, as well as doors which have a curved profile. The hanger assembly includes at least two separate tubular bearing segments, each containing a bearing means such as a ball bushing bearing. A suitable ball bushing bearing is available from Thomson Industries, Inc. of Manhasset, N.Y., under the trade name xe2x80x9cSuper Smart Ball Bushingxe2x80x9d bearing, which is available with or without integral wipers. The tubular bearing segments slide along a cylindrical rod that is easily pinned in place above the entry portal of the transit car.
The tubular bearing segments are mounted, for example by welding, to the hanger bar to which the sliding door is directly or indirectly attached. The manufacturer can select the locations along the hanger bar where the tubular bearing segments are mounted by taking into consideration such factors as the location of door hanger support points above the entry portal of the transit car, the location where the sliding door interfaces with an adjacent sliding door, the horizontal width of the door, and the distance that the door must travel along the cylindrical rod. Although these parameters may change depending on each particular size and type of transit car door, the same components can advantageously be used to manufacture the hanger assembly. The manufacturer need not maintain an inventory of separate tubular bearing segments depending on the particular dimensions of the door. Instead, the tubular bearing segments, which can be the same size for many different sizes and types of transit car doors, can advantageously be welded or otherwise secured to certain locations along the hanger bar as warranted by the parameters discussed above.
The hanger bar to which the tubular bearing segments are welded (or otherwise secured) may be a conventional hanger bar, such as shown in U.S. Pat. No. 3,740,898 (with a modification of the hanger bar in which the upper portion is preferably changed to interface with each of the tubular bearing segments, such as by milling depressions in the top of the hanger bar to receive the tubular bearing segments prior to welding, so as to minimize the overall height of the assembly). The hanger bar could also be of other profiles, such as the one shown in FIGS. 1 and 3 of U.S. Pat. No. 4,854,078. The cylindrical rod along which the tubular bearing segments slide is pinned to the top of the frame of the entry portal of the transit car chassis, preferably within a housing or behind an access panel so as to normally be hidden from view. The manner of pinning the cylindrical rod to the top of the frame can be similar to the manner in which U.S. Pat. Nos. 3,740,898 and 4,854,078 showed brackets (used in those patents to support and confine ball bearings) bolted to the top of the frame by a simple nut, washer, and bolt configuration. The manner in which certain embodiments of the present invention accomplishes these and other advantages over the prior art are described in the Detailed Description of Exemplary Embodiments, with reference to the drawings.